Views 3 exposed sort - default sort not applied

I am using Views 3.x-dev with a content pane to display a grid of products (Ubercart 2). I have three exposed sorts:

1. Node: Post date
2. Product: Sell price
3. Node: Title

I would like the default sort to be "Post date". Example: when the page initially loads, I want the products to be sorted by Post date (ASC). Although this is not currently happening. When I click the "Post date" exposed sort, it sorts them correctly, but changes the order (as opposed to the initial order).

How do I get it to default sort to "Post date"? If I remove the other two sorts, and make "Post date" NOT exposed, I achieve my goal.

I have tried adding an additional "Post date" sort that is not exposed, but this does not work.

Any ideas?

Please let me know if I should post my View code.

Thank you.